updated the release notes, tuned the release docs
Bumping to next rev
added method to check a plugin's version
require version 4.0 or later of the warnings plugin because the XML format changed since version 3.28
added a hint to the docs
Added spec element to GhprbTrigger.

By default, the GhprbTrigger XML element generated does not contain a <spec> element. When this element is not present, Jenkins will not use the trigger (tested with Jenkins v1.565, Git client plugin v1.9.1, Git plugin v2.2.1, Github API plugin v1.44, Github Authentication plugin v0.16, Github plugin v1.8, Github Pull Request Builder plugin v1.12).

By default, the spec element seems to get the same value as the cron element (when configured manually).
Merge pull request #210 from CoreMedia/minimum-plugin-version

Require Minimum Plugin Version
Merge pull request #211 from eveoh/pullrequestbuilder-spec-fix

Added spec element to GhprbTrigger.
Merge branch 'master' of https://github.com/jenkinsci/job-dsl-plugin into matrixjob_4